Phylum: Charophyta   Family: Desmidiaceae

Staurastrum punctulatum L.A. de Brébisson ex J. Ralfs 1848

A polymorphic species that occurs in 3- and 4-radiate forms. In apical view they are straight-sided.
Cell dimensions: L: 26-40 µm, B: 20.6-36 µm, Is: 8-12 µm; L/B: 1.20-1.41.
Widespread throughout Europe but not common in the Outer Hebrides. Found in moorland bogs and pools with variable acidity.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Ralfs, J. (1848). The British Desmidieae.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.